1. Field of the Invention
The present invention relates to a missile system for an aircraft for launching a guided missile in order to intercept and destroy a hostile threat to the aircraft.
2. Description of the Related Art
While most military fighter and bomber aircraft are heavily equipped with offensive firepower for attacking enemy targets, including enemy aircraft, the need for defensive measures to protect the aircraft from attack is equally important. There are two basic threats to a military aircraft during a hostile encounter; those being gun projectiles (which are unguided or ballistic in nature once fired) and guided missiles. There are generally three types of guidance seekers which are employed on guided missiles for use against aircraft. The three types of guidance seekers include infrared, radar and laser. Infrared (IR) and radar make up approximately 98 percent of all deployed guidance seekers on surface-to-air or air-to-air missiles. Laser technology has only recently been used in missile seeker guidance systems and to date has only been deployed on short range surface-to-air missile systems. IR seekers guide on the heat generated by the intended target, while advanced IR seekers guide on the temperature differential between the intended target and its background. Ordinarily, the air frame of a moving target, such as a missile or aircraft, will become hot due to friction when moving at high subsonic or supersonic speeds. The IR seeker can detect this temperature differential between the target and the surrounding atmosphere. On the other hand, radar guided missiles guide on the radar energy that is reflected from the target aircraft.
As the missile seekers have become more capable and sophisticated, so have the electronic warfare (EW) measures used to counter them. Every modern fighter is equipped with a radar warning receiver which is tuned to frequencies commonly used by hostile radars and missiles. When an enemy radar has locked onto a friendly aircraft, the radar frequency modulation changes. This change is displayed to the pilot in the cockpit as a missile "lock". The pilot then has to decide on a course of action to defend against this potential threat. The pilot can ignore the missile "lock", try to disrupt or deceive the hostile missile's guidance system by transmitting similar signals back to the missile, or the pilot can deploy bundles of chaff. Chaff is highly reflective to radar and creates an electronic "cloud" that may confuse or disrupt the missile's guidance seeker. Chaff can be highly effective, but is only carried in limited quantities and is only effective for a short range and time period, since the deploying aircraft usually flies out of a protective area soon after deployment of the chaff.
IR guided missiles present several complications to a pilot who must defend against them. Since the IR seeker is passive in nature (i.e., it does not emit radio waves that can be detected by the fighter's radar warning receiver), a pilot frequently does not know if one has been launched at him. Newly developed EW systems are able to warn a pilot of an IR guided missile's approach either by use of a tail mounted radar or an IR sensor that detects the heat from the missile's rocket motor. The primary problem which EW systems must be designed to overcome is the ability to correctly identify the type of threat seeker, either radar, IR, or laser, and then use specific types of counter-measures, either electronic techniques or expendables like chaff and flares. IR seekers can be decoyed away from the target aircraft by IR jammers that confuse the seeker. Alternatively, flares can be used which present a more intense heat source than the target aircraft, causing the missile to be diverted towards the flares and enabling the aircraft to maneuver away from danger. Electronic techniques are potentially effective, but require dedicated and expensive electronics. Expendables, such as chaff or flares, are fairly inexpensive, but must be carried in large numbers in order to be fully effective. Additionally, chaff and flares only work against one type of seeker, chaff being effective against radar and flares being effective against IR seekers. At this time, there is no identified EW or expendable technique that will detect and decoy laser guided missile seekers. Both electronic counter-measures (ECM) and expendables take up valuable aircraft volume which could otherwise be used for arsenal. Most importantly, ECM and expendables are both strictly defensive in nature and neither technology is capable of being used offensively to destroy hostile aircraft or missiles.
While IR guided missiles have been available since World War II, technical advances that allowed the missiles and guidance systems to be miniaturized have only recently become available. Because of these recent developments, two classes of IR missiles have evolved. The first was designed to be mounted on aircraft to engage other aircraft. The Sidewinder is the most common of this type used on aircraft. The U.S. version of this type weighs approximately 150 pounds, is 5-6 inches in diameter and is about 5 feet long with large fixed control fins and wings. The second type of IR missile is man-portable and is primarily used by soldiers to engage hostile aircraft. The Stinger is the most common of this type. The U.S. version weighs approximately 40 pounds in its launch tube, is 3-4 inches in diameter and is about 3 feet long with collapsible control fins/wings. The primary effective difference between these two types of missiles is performance. The Sidewinder carries a much larger warhead, has 2-3 times more range, flies at higher speeds and has the energy to make very high g turns. Both missiles are very capable of downing virtually any aircraft.
While both the Sidewinder and Stinger missiles are highly effective for their intended purpose, which is essentially offensive in nature, there still exists a need for a defensive-type missile system for use on an aircraft to defend against hostile threats, including enemy aircraft or missiles fired at the aircraft.